Should planter be "self-contained" or open at the bottom?

[hstraf]

Hello,
I want to build a cement block planter down one side of my driveway. So it would be about 2 feet high by 1.5 feet depth (inside measurement) by 40 feet long. On the house side, it would spread out to a big square planter next to the house that is around 6 feet on each side. This part of the planter would be about 4 feet high.

So kind of like this:

                                ______________
                               |              |
                               |              |
                               |              |
_______________________________|              |  (This part would be 4ft high by 6ft by 6ft.)
______________________________________________|
This part about 2ft high by 1.5ft depth)

Should I leave the bottom of the planter "open" to the dirt (currently grass) below the planter? Or should I put plastic around the entire inside of the planter so it is completely self-contained and isolated from the dirt under the planter?

Also, how should I "fill" the planter? Should I just put regular dirt into it? Or rocks at the bottom, then some sand, and then planting dirt on top? Will the cement blocks "leech" out the water from the dirt?

I live in a warm climate (a Mediteranean island) and will have plants that don't need much water. I'll probably have an olive tree or small palm tree in the middle of the square part, and then small shrubs and bushes around it and down the driveway side. There will be a simple drip irrigation system on a timer to provide the water.

Thanks for any advice!

 

[R.R.]

I live in a warm climate (a Mediteranean island)

Illes Balears by any chance?

Welcome to the forums!

 

[hstraf]

Illes Balears by any chance?

Nope. Corsica.

 

[R.R.]

I bet it's an awesome place

 

[Chuck]

If I were to do this I would leave it open at the bottom and put a double layer of weed cloth in the bottom. This thing must drain. As for as the soil why not just an even mixture of good compost, top quality potting soil and landscape mix

 

[hstraf]

Thanks!

Would you put plastic around the inside sides, so the dirt does not directly touch the cement blocks? (I'm wondering if that will help retain moisture in the dirt so it doesn't leech out as quickly during the hot weather?)

 

[Chuck]

Thanks!

Would you put plastic around the inside sides, so the dirt does not directly touch the cement blocks? (I'm wondering if that will help retain moisture in the dirt so it doesn't leech out as quickly during the hot weather?)

Doing that would act a a moisture barrier and that is good, but it would also I think reduce oxygen in the soil. I don't know for sure one way or the other

 

[firelily99]

I agree with Chuck, the layers of weed cloth are what I would do in that situation. I don't like to use anything that has plastic in it in my garden, whether or not it is visible.

 

[Lostvalleyguy]

You definitely want to let the water flow through so I would not recommend sealing it up with plastic. As the planter is fairly deep, weeds will not grow up from below but encroaching roots may try to take advantage. A layer of loose brick or paving stones will inhibit roots growing up into the planter from below while providing adequate drainage. Rocks or gravel will work but will not be as effective at physically blocking root growth from below. Landscape fabric will drain but it will only be effective as a barrier from what grows beneath for a few years.

 

[Rosyrain]

I agree, leave it open. This way if you over water your plants, then the excess water will drain out the bottom quicker and you will not waterlog and drown your plants.